This invention relates to fluid-actuated friction devices including selectively engageable friction members wherein the engaging pressure is decreased by a pressure control means responsive to slip speed, thereby reducing engagement shock.
Presently used selectively engageable multi-plate friction clutches or brakes have a first set of plates splined to a first torque transmitting member and a second set of plates interleaved with the first set and splined to a second torque receiving member. The plates are generally brought into engagement by means of a fluid-actuated clutch piston, and engagement shock is generally an important factor during dynamic engagement. Various methods to alleviate shock are in common use, including hydraulic oils and friction materials developed for desirable engagement characteristics and various devices used to control the rate of pressure rise. These methods provide conditions for clutch engagement which accomodate shock problems, but are not responsive to a change in parameters occurring in use or during the life of the mechanism.
During the engagement of the multi-plate clutch, the relative speed between the driving and driven plates, or slip speed, changes from maximum to zero. As the speed of the driven plates approaches that of the driving plates, a reduction in applied hydraulic pressure on the clutch piston would further reduce engagement shock. The proper moment for reduction of applied hydraulic pressure will vary with the duration of the engagement and cannot be pre-programmed.
A friction device having pressure control means responsive to slip speed for reducing the applied pressure as slip speed approaches zero would thus be quite useful and effective in minimizing engagement shock.